Sure, but those are two different things. Offsite is good to protect against natural disasters (or attacks, or...), offline is good to protect against digital disasters (ransomware, admin mistakes, etc.)

Tape libraries are a way to store offline backups, but they don't have to be offline and aren't the only way to run a backup solution. They are a way to store data in bulk for cheap. They are also a way to help protect against technological changes (if all your backups are on 5 1/4" floppy discs and you can't find any 5 1/4" floppy drives, then your backups are no good).

Some people like to use a 3-2-1 solution (3 copies, 2 different technologies, 1 offsite), but that doesn't specifically mention anything about offline, which is critical for these types of situations, and the exact solution has many different correct answers.